Laboratory experiments have shown that mosquito blood-feeding frequency decreases with increased access to sugar. The proposed research will determine 1) whether this blood/sugar interaction occurs under field conditions, 2) how sugar feeding changes the gonotrophic cycle, and 3) why some mosquito species are strongly affected by sugar. The answers will explain the relations between blood feeding, sugar feeding, and oviposition in behavioral terms, forming a basis for identifying medically important species whose ability to transmit pathogens is reduced by abundant plant sugar. This information is useful for assessing and reducing the risk of vector-borne disease. An automated system will be developed to record long series of blood-feeding, sugar-feeding, and oviposition events, using electronic sensors and time-lapse infra-red video. The disease vectors Anopheles quadrimaculatus and Aedes triseriatus, representing opposite extremes in the degree of blood/sugar interaction, will be compared in high- and low-sugar environments, to test 4 hypotheses explaining the expression of this interaction. Field experiments in large enclosures will be used to determine diel rhythms, mean frequencies, and temporal relationships of the behavioral events, and to measure sugar's effect on biting frequency under natural physical conditions. Temporal patterns of the behavioral events of isolated females will be monitored in the laboratory while they undergo a series of free-running gonotrophic cycles; the data will be analyzed to obtain a precise behavioral explanation for the effect of sugar on biting frequency.